I would think no more than 1-2 thousands (.025mm - .05mm) larger than the hub would be about right. That's sort of typical shaft to bearing clearance for machinery. The spacers you found are about .015 undersized to the hub, I don't think those will fit for you.
Couple of options; call Motorsports tech and see if they can custom make something. I know they do a lot of custom stuff at their facility.
Or, buy the ones you found, take them and your hubs to a local machine shop and have them open up the bore on the aluminum hub rings. If it were me, I would have the machine shop make them with an interference fit and press them on. That way when you remove the wheels for any reason the hub spacers stay in place.
Heck, the machine shop can probably make what you want from scratch just as easy and skip the extra step. Give them the trailer hubs and a wheel then let them go to town. This would guarantee everything fits up as planned and you could have them done in steel instead of aluminum.
I would definitely want everything in hand to verify measurements before proceeding. Not sure I trust the precision of the trailer hubs...
This of course assumes that you are still going to use the Currie metric studs and Toyota OEM lug nuts.